Method and apparatus of production of noncontaminated plasmoids

ABSTRACT

A method for producing and/or heating a plasmoid, consisting in disposing a target at a first conjugate focal point of a closed chamber which constitutes a mirror system and in producing at least at a second focal point which is conjugate with said first focal point a substantial release of electromagnetic energy in the form of a pulse of very short duration, said energy being focused on said target which is thus heated to a high temperature.

I United States Patent llll 3,562,530

[72] inventors Terenzio Consoli [51] Int. Cl G21g 3/00 LaCelle SaintCloud: [50] Field of Search .l 250/845 21 A l N gg ggj Maggy FrancePrimary Examiner-Archie R. Borchelt i Janzz 1968 AssistantExaminer-Mort0n J. Frome E gf 9 1 Attorney-Craig, Antonelli, Stewart &Hill [73] Assignee Commissariat A LEnergie Atomique Paris, France [32]Priority Feb. 2, 1967 France ABSTRACT: A method for producing and/orheating a 93498 plasmoid, consisting in disposing a target at a firstconjugate focal point of a closed chamber which constitutes a mirrorsystem and in producing at least at a second focal point which [54]METHOD AND APPARATUS 0F PRODUCTION OF is conjugate with said first focalpoint a substantial release of NONCONTAMINATED PLASMOIDS l7 Claims, 8Drawing Figs.

US. Cl 250/845 electromagnetic energy in the form ofa pulse of veryshort duration, said energy being focused on said target which is thusheated to a high temperature.

'PATENTED FEB 9m SHEET 1. [1F 4 v 1NVENTOR$ TERI/V210 CU/VSOL/ LUf/E/VSLAHH ATTORNEYS PATENTEI] FEB 9m 3552 530 sum 2 [IF a AAAAAA YsPA-TENTEn FEB 9mm 3 562 530 SHEET 3 BF 4 BY a ATTORNEY METHOD ANDAPPARATUS OF PRODUCTION OF NONCONTAMINATED PLASMOIDS This invention isconcerned with a method of production and/or of heating ofnoncontaminated plasmoids and a device for the practical application ofsaid method or a like method.

Many methods have already been proposed or employed for producing denseand hot plasma bursts, or so-called plasmoids. Among these methods canbe mentioned the formation of convergent shock waves which are generatedfrom explosion cylinders, in which an explosion permits ultrarapidcompression of an intense magnetic field and produces bursts of plasma,or plasmoids, of very high density. Unfortunately, as soon as such aplasma is formed. it is contaminated by the impurities contained in theexplosive charge or in the conduc- 7 tive metallic jacket which isenclosed by the explosive.

For the purpose of generating plasrn oids, use has also been made of alaser beam focused on a gaseous target or on a mechanically supportedsolid target which is maintained in levitation or which falls in a freedrop. However, when only a single laser is employed, the energy which isavailable at the focal point of the focusing dioptric system isrelatively small (less than one kilojoule) and it would have very costlyincrease in this energy by at least one order of magnitude.

An alternative method which appears to be very attractive consists ofreplacing the limited energy source formed by a parallel beam of apulsed laser with a noncoherent source which generates higher energylevel pulses in other words, the operation of the non coherent source iscarried out with free" flashes of very substantial power. It is also anadvantage to prevent any variation in the focal distance of a dioptricfocusing system as a function of the wavelength ofthe incidentradiation.

On the basis of the well-known fact that kinetic energy can be convertedto radiant energy with a high degree of efficiency (of the order of 90percent), the present invention is directed to a method of producingplasma burst and to devices of composite structure wherein a mirrorsystem, is employed so as to dispense with the need for preventingvariation of the focal distance as a function of incident radiation thewavelength.

With this object in view, the invention proposes a method whichcomprises disposing a target at a first of the conjugate point of aclosed chamber which constitutes a mirror system and in producing atleast at one point which is conjugate with said first point asubstantial release of electromagnetic energy in the form ofa pulse ofvery short duration, this energy being focused on said target which isthus heated to a high temperature,

A better understanding of the invention will be gained from thefollowing description in which various nonlimitive applications of theinvention are illustrated by way of example taken in conjunction withthe accompanying drawings, in which:

FIG. 1 is a diagrammatic view of a device according to the invention asshown in cross section along a plane of symmetry which passes throughthe foci;

FIGS. 2 to 8, which are similar to F107 1, show alternative forms ofconstruction of the device of FIG. 1.

In one embodiment which is illustrated in FIG. 1, the closed chamber 10has the shape of an ellipsoid of revolution. Said chamber is confined bya mass 12 of concrete which is buried underground and is endowed withsufficient mechanical strength to withstand the shock waves generatedduring operation. The concrete structure 12 is fitted with an internallining 14 formed of a material which has a high coefficient ofreflection. Said lining 14 may consist ofa burnished metallic skin or ofa coating of silica which is vitrified by means ofa preliminary seriesof explosions generated within the chamber 10. Said chamber 10 isequipped with means 15 for producing therein a high vacuum (of the orderof 10- Torr), as well as with means for measuring pressure ortemperature, and with viewing windows.

There is suspended at a first focus or focal point of the chamber aspherical charge 16 of a high explosive (such as TNT, for example) whichis intended to constitute a radiation source and which is associatedwith an electric circuit 18 for initiating an explosion. as illustrated.electric circuit 18 may comprise a capacitor-source circuit. Thespherical charge may also be suspended from triggering wiresv Acryogenic device not shown and which may comprise a lock-chamber, servesto introduce and maintain a target at the second focal point of achamber 10 for a short predetermined time interval. The target maycomprise a fragment of solid deuterium or of a solid deuterium tritiummixture.

During operation, the device shown in FIG. 1 is triggered by closing thecapacitor 19 of the circuit 18 The spherical charge 16 of high explosiveconstitutes a spherical source of radiant energy which produces aspherical shock wave and an associated radiation which is reflected fromthe lining element 14 and focused at the target 20, thereby producingintense ionization and forming a neutron burst as a result of the fusionprocess which takes place at the target. Since the time of transport ofimpurities from the first focal point to the second is longer than thetime of transfer of the radiation energy. the effect of the radiation(ionization and heating) is more rapid than the effect of contaminationby the impurities. The time interval or delay T which elapses betweenthe arrival of radiation and the arrival of material impurities at thesecond focal point can be estimated; in this connection, with a focaldistance of a few meters, an eccentricity of less than one-half andcontaminating ions having an energy of 10 keV, time intervals of theorder of one-tenth of a microsecond are obtained.

The method is obviously of real practical interest only if twoconditions are complied with: on the one hand. the radiation produced bythe explosion must be such that it is reflected from the wall so thatlosses prior to focusing on the second focal point are not excessive;and on the other hand, it is necessary to ensure that an energy whichhas a high gradient in the vicinity of the second focal point can befocused thereon.

Insofar as the first condition is concerned, it is known that a plasmawhich is created by an explosion in a gas behaves practically as a blackbody. In consequence, the total radiant energy is given by the relation:

Z w=f oo()t,'l')dlt=o"l' (1) wherein 0' 5.679 X l0-w/cm. (C. Theradiation has a maximum intensity at the wavelength A A,,.T=2.898 IOA.K(2) In point of fact, the plasmas created by explosives in compressedgases can easily attain a temperature above 100 eV. Thus, approximatelypercent of the energy of the radiation corresponding to shortwavelengths (in the visible range and beyond the visible range) arepropagated in the ionized medium which is created around the explosionzone at the velocity of light and are subjected to reflection from thewalls of the ellipsoidal chamber.

So far as concerns the second condition mentioned above, thecharacteristics of the plasma which is produced at the second focalpoint by an energy source IE placed at the first focal point are givenby the relation:

2: 2E1 N2T2=-3-K-5 m)4 t wherein N is the total number of charges at thesecond focal point;

T is the energy of the ions, in K;

0' is the radiation constant; (o'=5.679 X 10- w./cm. (degree);

It is the Bolzmann constant, 1.38 X 10- N is the total charge number inthe region of the first focal point;

S, is the surface area of the radiant spherical volume at the origin ofthe time coordinates (namely that of the spherical explosive charge);

a is a coefficient of transfer efficiency which is variable between 0and 1, depending on the state of the surfaces.

It is apparent that N T has no theoretical limitation and is solelydependent on the energy E,.

For example, in the case of an efficiency of 40 percent, when aspherical charge of TNT having a radius of 3 cm. is exploded at thefirst focal point of a chamber having a vacuum of IO Torr and aspherical pellet of solid D having a radius of 2 cm. is provided at thesecond focal point of said chamber, a burst of 10 neutrons is produced.The burst would be l neutrons with a deuterium-tritium mixture.

When a solid deuterium-tritium target is employed as has just beenindicated, a high degree of vacuum is maintained throughout the chamber.However, when it is desired to employ two different atmospheres aroundthe spherical charge of explosive 16 and around the target 20respectively, it is merely necessary to provide a radiation transparentwall 21 between the charge 16 and the target 20. As shown inchain-dotted lines in FIG. 1 such a wall 21 divides the chamber into twocompartments. By employing such a wall it is possible, for example, toproduce a high vacuum solely within the compartment which surrounds theexplosive sphere while maintaining a deuterium atmosphere within thecompartment which contains the target. It is also possible to place theexplosive sphere in a rare-gas atmosphere (xenon or xenon-kryptonmixture) and to place the target in a deuterium atmosphere.

The presence of the wall 21 makes it possible not only to maintain twoatmospheres within the chamber but also to prevent contamination of thetarget 16 by the ions which are derived from the explosive sphere 16. Inthe case in which only the second result is sought, it is possible toemploy a magnetic field having lines of force which are transverse tothe major axis of the ellipsoid so as to constitute a barrier whichprevents the passage of charged particles derived from the explosivesphere. Said magnetic field could also confined the plasma which iscreated by the point, thereby initiating the explosion of the sphericalcharge 16,,: The heat energy and light energy emitted by the explosivecharge are reflected from the wall 14,, and focused onto the alreadypreionized target 20,, so as to produce a burst of plasma and ofneutrons.

FIG. 3 shows another alternative form in which the explosive sphere 16,,is replaced by a spark-gap 16,, which is brought to a potential veryslightly below the disruptive potential by a capacitor bank. In thiscase also, triggering is effected by means of a pulsed laser.

When it is found desirable to divide the chamber into two compartmentsby means of a material wall, all of the foregoing arrangements make itnecessary to provide a wall of substantial diameter. However, it issomewhat difficult to provide a wall having both a substantial diameterand a sufficient strength to withstand an explosion. In order to solvethis problem, the arrangement shown in FIG. 4 can be adopted. Thus, thecentral portion of the chamber is narrowed by means of an internalportion 26 of increased thickness which is delimited by a segment ofellipsoid 28 and two segments of hyperboloids 30 and 32 which arehomofocal with the wall 14 in this manner the wall 21, has a smalldiameter the focusing thereof remains total by virtue of the well-knownproperties of homofocal conics. There is shown by way of example in FIG.4 a light beam which has been reflected a number of times before beingfocusedon the target 20,.

Since the extreme case of a hyperboloid is constituted by the midplanebetween the two foci, one of the terminal faces (such as the face 30,for example) can be flat and located at a point midway between thesphere 116, and the target 20, (the face 30 being indicated in chaintarget. Furthermore, in the case in which the magnetic field is ofsufficient amplitude to ensure that the charged particles having thehighest energies are capable of passing through it, it could be madepossible to recover the energy by Hall effect.

Among the alternative embodiments of the invention which can becontemplated, a few variants are illustrated very diagrammatically inFIGS. 2 to 8, in which the walls limiting the chamber are merely shownin outline.

In the device shown in FIG. 2, an explosive sphere I6, is againsuspended at the first focal point of the chamber 14 In this embodiment,the explosive is not triggered by an electric circuit, but by aconcentration of energy from a laser beam. To this end, the chamber isfitted with a dioptric system 22 which serves to focus the beam of alaser 24 onto the second focal point at which the target 20,, islocated. Said target can again be either suspended from a wire (notshown) or released in free fall, or maintained in levitation by means ofelectrodes (not shown). The target can be formed by a fragment ofdeuterium or a mixture of deuterium and tritium in the solid state inorder a vacuum is maintained within the entire chamber.

During operation of the device shown in FIG. 2: the laser 24 istriggered and the resulting flash is focused on the point 20,, by thedioptric system, whereupon a preionization of the target takes place.The image of the laser beam or of the burst produced by the laser (witha vacuum of the order of one mil limeter of mercury) is then reflectedalong the walls 14,, of the chamber and focused on the first dottedlines in FIG. 4).

In the case in which it proves unnecessary to establish a materialseparation between the target and the spherical explosive charge (thatis to say when the atmosphere can be the same, but when it is desired toavoid any direct path between the spherical charge and the target), itis possible to employ the device illustrated in FIG. 5, which can beconsidered in some degree as being symmetrical with that of FIG. 4.Thus, the device comprises a central obstacle 34 delimited by reflectingwalls having the shape of segments of an ellipse 28,, and ofhyperboloids 30,, and 32,, which are homofocal with the wall 14,,. Itshould be noted that, especially in the case of an elongated ellipsoid,it is possible by means of this arrangement to delimit a chamber ofsubstantial volume around the spherical charge 16,, and a chamber ofsmall size around the target 20,,.

In the embodiment illustrated in FIG. 6, use is made of the caps locatednext to the apices of two paraboloids which have a common axis and whichare joined to each other by a cylindrical portion so as to form a closedchamber. The spherical charge 16,. and the target 20, are located at thefocal points of the chamber embodiment. This makes it possible to reducethe maximum diameter of the device at the price of a loss of energy,inasmuch as that portion of the energy which is emitted outside thesolid angle limited by the paraboloid cap is evidently not focused onthe second point. Similarly, instead of an ellipsoidal chamber, if anenergy loss resulting from inadequate focusing can be accepted, it ispossible to make use of two ellipsoid segments surrounding the focalpoints and joined to each other by a cylindrical portion.

It is also apparent that a plurality of mirror systems can be associatedeither in series or in parallel. By way of example, FIG. 7 shows achamber in which the wall 14, is constituted by four segments ofellipsoids having a common focal point. In the embodiment which isillustrated, the ellipsoids are identical and of revolution and the fourother focal points are disposed at right angles to each other about thecommon point. Four spherical explosive charges 16, which are located atthe four separate points are triggered simultaneously. Triggering can beperformed by focusing a laser beam on the common focal point, said beambeing directed along a plane at right angles to that of FIG. 7. As thusdesigned, this arrangement would produce a loss of energy as a result ofthe absence of a cap on each ellipsoid, this loss being ofcorrespondingly smaller magnitude as the ellipsoids are of greaterlength. This loss is avoided by providing screens 30fconstituted by capsor segments of hyperboloids which are homofocal with the ellipsoids andwhich extend through thesolid angle having a vertex 16f. Said segmentsare applied against the line of intersection of the ellipsoid consideredwith the adjacent ellipsoids. Without producing any appreciable loss ofenergy, the screens can be supported by full members, provided that saidmembers do not project beyond the cones which are applied against theedges of the screens 30f, the vertices of said cones each beingconstituted by the corresponding focal point 16f.

FIG. 8 gives one example of an association in series of a plurality ofellipsoids which constitute a chamber 14g; in this case also, screens30g, 30g, 30"g in the form of caps of hyperboloids which are homofocalwith the ellipsoids are provided for the purpose of preventing energylosses.

Generally speaking, it can be noted that any portion which is removedfrom an ellipsoid of revolution can be replaced by any one of aninfinite number of segments of surface cut from a hyperboloid. Thehyperboloid segments must be homofocal with the ellipsoid by a conewhich is applied against the contour of the removed portion, the vertexof said cone being constituted by the focal point at which the emissiontakes place; by way of illustration, hyperboloids of this type are shownin chain-dotted lines in FIG. 5.

It is readily understood that the invention is not limited solely to theembodiments which have been illustrated and described by way of exampleand 'that the scope of this patent extends to alternative forms of allor part of the arrangements herein described which remain within thedefinition of equivalent means as well as to any application of sucharrangements such as, for example, the generation of energy by Halleffect by producing a periodic magnetic field having an amplitude suchthat the paths of the charged particles which have the highest energiesare simply deflected but not stopped between the target and the energysource.

We claim: 1. A method for producing an outburst of nonpolluted plasmawhich comprises:

providing at a first focal point of a mirror system in a closed chambera target comprising a substance which will form a plasma under theinfluence of intense heat; and

liberating at a second focal point of said mirror system a pulse ofelectromagnetic energy of short duration, said second focal point beingthe conjugate of said first focal point so that the energy liberated atsaid second focal point is reflected by said mirror system and focusedon said target to heat said target and form a plasma therefrom which isfree from the impurities associated with the energy pulse.

2. The method of claim 1, wherein said pulse of electromagnetic energyis produced by an explosive charge.

3. The method ofclaim 1, wherein said pulse of electromagnetic energy isproduced by an electric arc.

4. The method of claim 2, wherein a laser beam is impinged on saidtarget and then reflected by said mirror system and focused on saidsecond focal point to initiate the explosion of said explosive charge,said target thus undergoing a preionization immediately prior to saidexplosion.

5. The method of claim 3, wherein a laser beam is impinged on saidtarget and then reflected by said mirror system and focused on saidsecond focal point to initiate said electric arc, said target thusundergoing a preionization immediately prior to said explosion.

6. The method of claim 1, wherein a magnetic field is establishedbetween said first and second focal points to oppose the passage towardsaid target of charged particles originating at said second focal point.

7. The method of claim 6, wherein the intensity of said magnetic fieldis such that the most energetic of the charged particles of the sourceof electromagnetic energy can pass through said magnetic field and thata portion of the kinetic energy thereof is converted into electricenergy by the Hall effect.

8. A device for producing a plasma outburst which con prises:

a closed chamber including: a catadiotric system having a first focalpoint and at least one second conjugated focal point;

a plasma forming target disposed at said first focal point.

and

means for liberating a short burst ofelectromagnetic energy at saidsecond focal point.

9. The device of claim 8, wherein said chamber has an ellipsoidal confiuration.

10. The evice of claim 8, wherein said chamber comprises twoparaboloidal sections having a common axis and being interconnected bymeans ofa substantially tubular member.

11. The device of claim 9, wherein said chamber is constricted in thecentral portion thereof by an annular enlarge ment of the chamber wall,said annular enlargement being defined by portions of surfaces ofrevolution whose generatrices are homofocal cones of said wall.

12. The device of claim 10, wherein said chamber is constricted in thecentral portion thereof by an annular enlargement of the chamber wall,said annular enlargement being defined by portions of surfaces ofrevolution whose generatrices are homofocal cones of said wall.

13. The device of claim 9, wherein said chamber is separated into twocompartments occupied by different atmospheres by a material wall whichis transparent to electromagnetic radiation.

14. The device of claim 10, wherein said chamber is separated into twocompartments occupied by different atmospheres by a material wall whichis transparent to electromagnetic radiation.

15. The device of claim 8, wherein said chamber is comprised of aplurality of ellipsoids each having one common focal point.

16. The device of claim 15, wherein each of said ellipsoids is providedwith a hyperboloidal reflecting surface screen which is homofocal withthe noncommon focal point of each respective ellipsoid.

17. The device of claim 8, wherein said chamber is under a high vacuum,and wherein said target is a solid mass selected from the group ofdeuterium, tritium and mixtures of deuterium and tritium.

2. The method of claim 1, wherein said pulse of electromagnetic energyis produced by an explosive charge.
 3. The method of claim 1, whereinsaid pulse of electromagnetic energy is produced by an electric arc. 4.The method of claim 2, wherein a laser beam is impinged on said targetand then reflected by said mirror system and focused on said secondfocal point to initiate the explosion of said explosive charge, saidtarget thus undergoing a preionization immediately prior to saidexplosion.
 5. The method of claim 3, wherein a laser beam is impinged onsaid target and then reflected by said mirror system and focused on saidsecond focal point to initiate said electric arc, said target thusundergoing a preionization immediately prior to said explosion.
 6. Themethod of claim 1, wherein a magnetic field is established between saidfirst and second focal points to oppose the passage toward said targetof charged particles originating at said second focal point.
 7. Themethod of claim 6, wherein the intensity of said magnetic field is suchthat the most energetic of the charged particles of the source ofelectromagnetic energy can pass through said magnetic field and that aportion of the kinetic energy thereof is converted into electric energyby the Hall effect.
 8. A device for producing a plasma outburst whichcomprises: a closed chamber including: a catadiotric system having afirst focal point and at least one second conjugated focal point; aplasma forming target disposed at said first focal point; and means forliberating a short burst of electromagnetic energy at said second focalpoint.
 9. The device of claim 8, wherein said chamber has an ellipsoidalconfiguration.
 10. The device of claim 8, wherein said chamber comprisestwo paraboloidal sections having a common axis and being interconnectedby means of a substantially tubular member.
 11. The device of claim 9,wherein said chamber is constricted in the central portion thereof by anannular enlargement of the chamber wall, said annular enlargement beingdefined by portions of surfaces of revolution whose generatrices arehomofocal cones of said wall.
 12. The device of claim 10, wherein saidchamber is constricted in the central portion thereof by an annularenlargement of the chamber wall, said annular enlargement being definedby portions of surfaces of revolution whose generatrices are homofocalcones of said wall.
 13. The device of claim 9, wherein said chamber isseparated into two compartments occupied by different atmospheres by amaterial wall which is transparent to electromagnetic radiation.
 14. Thedevice of claim 10, wherein said chamber is separated into twocompartments occupied by different atmospheres by a material wall whichis transparent to electromagnetic radiation.
 15. The device of claim 8,wherein said chamber is comprised of a plurality of ellipsoids eachhaving one common focal point.
 16. The device of claim 15, wherein eachof said ellipsoids is provided with a hyperboloidal reflecting surfacescreen which is homofocal with the noncommon focal point of eachrespective ellipsoid.
 17. The device of claim 8, wherein said chamber isunder a high vacuum, and wherein said target is a solid mass selectedfrom the group of deuterium, tritium and mixtures of deuterium andtritium.